1. Field of the Invention
The present invention relates to a phase sampling protection device, and more particularly, to a phase sampling protection device using phase sampling technique to determine whether the tube functions normally to improve the accuracy in detection.
2. Description of the Prior Art
FIG. 1 illustrates a prior art tube circuit, which substantially comprises a tube circuit 91, a detection circuit 92 and a protection circuit 93, wherein detection circuit 92 comprises a RC rectifying circuit 921 and a comparator 922; detection circuit 92 coupling between the low-voltage end of transformer 911 of tube circuit 91 and protection circuit 93 to directly detect a low-voltage end signal of transformer 911 of tube circuit 91, RC rectifying circuit 921 rectifying the low-voltage end signal into a DC signal and outputting it to comparator 922, then comparator 922 comparing the DC signal with an reference signal to determine whether to drive protection circuit 93 or not, in order to drive protection circuit 93 to shut down the power supply of tube 912 to keep transformer 911 from burning down and other safety issues from happening.
However, in the above-mentioned detection method, the low-voltage end current of transformer 911 is current Io, which equals to the sum of current Ic1 (generated by high-voltage end capacitor C1), current Ic2 (generated by stray capacitor C2) and current Ic3 (generated by line coupling capacitor C3). The values of Ic1, Ic2, Ic3 will change as the voltage of tube 912 varies, so when tube 912 fails, the voltage of high-voltage end will increase due to no negative impedance effect from tube 912 to pull down the voltage, then Ic1 and Ic3 will also increase (Ic2=0 when tube is open circuit), therefore, the low-voltage end current Io will not drop significantly when tube 912 fails, making it difficult for comparator 922 of detection circuit 92 to determine whether tube 912 functions normally only by detecting the low-voltage end current signal, resulting in failure to drive protection circuit 93 and failure to keep transformer 911 of tube circuit 91 from burn down or other safety issues from happening.
Therefore, the above-mentioned prior art detection method presents several shortcomings to be overcome.
In view of the above-described deficiencies of prior-art tube circuit, after years of constant effort in research, the inventor of this invention has consequently developed and proposed a phase sampling protection device in the present invention.